Pencil plunger



F. C. DELI PENCIL PLUNGER Filed sept. l24, 19:54

Patented June 23, 1936 PATENT OFFICE PENCIL PLUNGER Frank C. Deli, Chicago, Ill., assignor to Autopoint Company, Chicago, Ill., a corporation of Illinois Application September 24, 1934, Serial No. 745,246

3 Claims.

My invention relates to pencils and particularly to the plunger or lead-advancing element thereof. Such a plunger, in its operable relation is shown in my prior Patent No. 1,682,070 of August 28, 1928.

Plungers of the described type that are commonly in use are of two kinds; rst, the kind such as is shown in the patent above identified in which the lead-engaging projections are formed for extruding the metal laterally by die action, and secon-d, the type in which a thread of common form is cut throughout the operable length of the plunger. Each of these types of plungers has disadvantages that are overcome in the construction illustrated herein. The novel lead-advancing element of my invention is intended for production by die casting, this process, ln its recently perfected form, enabling the production of plungers at a very low cost, and composed of metal that will withstand the strains incident to the contemplated use.

Furthermore, I am able to provide a theoretically correct design for the plunger; in other words, a design that is not practically possible of production, except by a. die casting operation. These points will be discussed in the following description.

The invention will be more readily understood by reference to the accompanying drawing, in which:

Fig. 1 is an elevation of a pencil plunger, greatly enlarged, constructed in accordance with my invention;

Fig. 2 is a view similar to Fig. l, taken at right angles thereto; and

Fig. 3 is an end view.

In the drawing it will be seen that the plunger body I0 is of substantial size and preferably circular in cross section. At its upper end it is provided with the usual wings II, that engage with corresponding grooves in a pencil body, whereby the plunger may reciprocate without rotation. At its lower end the stem I0 is somewhat reduced in diameter, as at I2, to provide a diameter substantially the same as that of the leads with which it engages, in order that the plunger may project through the outlet openingV for the lead in the tip. If the lead is to be completely ejected, it is essential that the lower end of the plunger be formed of the same diameter as the lead, and this has necessitated the formation of the entire plunger ofmaterial of this diameter, there being no practical method whereby the up- (Cl. 1Z0-18) per, or body portion that is subjected to the strains of operation may be formed of material of greater diameter than the lower portion. 'Ihis is made possible by the casting method of production.

Intermediate the ends of the plunger I provide threads of novel form, two of such threads, indicated at I3, being shown. These are half threads, being formed on only one side of the body I0. This construction greatly facilitates the `die casting operation, and the half threads function equally as well as full threads in the desired use. Furthermore, the shoulders I4, formed at the point of interruption of the threads, are relatively square, or abrupt, and have the eifect of cleaning out the spiral passageway in the tube in which the plunger operates. Thus small particles of lead are removed and prevented from interfering with the operation of the plunger.

While I have shown two of such half threads, it will be understood that more or less thereof may be provided as required; further, that other modifications may be made without departure from the spirit of my invention.

I claim:

1. A pencil plunger consisting of a body and a thread projection formed thereon, extending over only substantially one half of the circumference of the body, said projection being formed outside of the body without reducing the cross sectional area of the body at any point, and constituting the sole projection beyond the periphery of the body.

2. A pencil plunger consisting of a body and a plurality of projections thereon having the function of threads, said projections each eX- tending over only substantially one half of the circumference of the body, and being formed out- -side of the body diameter without reducing said diameter at any point, and constituting the sole projections beyond the periphery of the body.

3. A pencil plunger consisting of a body and a thread projection formed thereon, extending over only substantially one half of the circumference of the body, said projection being formed outside of the body without reducing the cross sectional area of the body at any point, said half thread presenting relatively square shoulders at its terminal points, and constituting the sole projection beyond the periphery of the body.

FRANK C. DELI. 

